The proposed experiments are designed to contribute to the understanding of neuronal relationships within cerebellar cortex in the context of the spatial pattern of tactile projections to the cerebellum. These experiments can be roughly divided into two categories, those continuing to explore the influence of granule cells on Purkinje cells, and those designed to explore the development and maintenance of the fractured somatotopic tactile projections maps in the granule cell layer. In the first set of experiments, the apparent differential influence on Purkinje cells of the ascending and the parallel segment of granule cell axons will be explored. We will use intracellular recording methods in an in vitro brain slice preparation to measure effects directly; electron microscopic techniques to describe the synaptic contacts these granule cell axon segments make on Purkinje cells; and new multi-single neuron recording techniques to look at granule cell effects in vivo. Rats and guinea pigs will be the experimental subjects. In the second group of experiments we will explore the effects on cerebellar tactile maps of peripheral lesions made early in the development of the rat and in adult rats. These experiments are intended to shed light on possible factors underlying map formation and maintenance. In general, both types of experiment will fill conspicuous gaps in knowledge regarding the functional organization of cerebellar cortex. Accordingly, the results will aid in ongoing attempts to interpret the functional significance of the unusual spatial organization of peripheral projections to this cortex and the overall role of the cortex in sensory-motor coordination.